class_docstr: A subgraph of a TensorFlow computational graph.
  
  TensorFlow graphs are often too low-level to represent our conceptual
  understanding of a model
  
  OverlayGraph can be used to represent a simplified version of a TensorFlow
  graph. Each node corresponds to a node in the original TensorFlow graph, and
  edges correspond to paths through the original graph.
code: def sorted(self, items):
      return sorted(items, key=lambda n: self.nodes.index(self[n]))
  
imports: from collections import defaultdict
  import numpy
  import tensorflow
label_desc: Use image node_id 10 for calling the OverlayGraph obj's underlying member method code with example usage: obj.sorted(items) and returns: sorted